Preparation of biotin via thieno [3,2c] isoxazoles

ABSTRACT

A process is disclosed for producing d-biotin from L cysteine via substituted thiens [3,2c] isoxazoles.

This is a division of application Ser. No. 75,360, filed Sept. 13, 1979,now abandoned, which in turn is a divisional of Ser. No. 946,675, filedSept. 28, 1978, now U.S. Pat. No. 4,189,586, which in turn is adivisional of Ser. No. 822,119, filed Aug. 5, 1977, now U.S. Pat. No.4,130,713.

BACKGROUND OF THE INVENTION

This invention relates to a process of preparing biotin fromL-(+)-cysteine. Biotin, vitamin H, is a natural product found largely inthe kidney, liver, egg yolk, milk and yeast. The compound is used toprevent symptoms of egg-white injury in experimental animals. Its primemedical use is in various dematitides.

Biotin has been prepared synthetically by Harris et al. (Science, 97,447 (1943) and Baker et al. (J. Org. Chem., 12, 167 (1947), amongothers. None of these syntheses, however, were commercially feasible.The first commercial synthesis of biotin resulted from the work ofGoldberg and Sternback (U.S. Pat. Nos. 2,489,235 and 2,489,236).

Previous biotin syntheses suffer from the disadvantages that racemicmixtures of intermediates, as well as racemic mixtures of biotin, areformed thus requiring costly and time consuming resolutions. Theseresolutions also lead to decreased yields of biotin. This disadvantageis obviated in the instant invention by use of cysteine as the startingmaterial. Cysteine, a natural amino acid is an optically active compoundwith the same absolute configuration as the C₄ -carbon of d-biotin, thebiologically active form of biotin. The process of the instant inventionproceeds without racemization in forming d-biotin, thus obviating theneed for resolution of the final product.

According to the instant invention, biotin is obtained in either theoptically pure d-form or as a racemic mixture from a relativelyinexpensive starting material. When d-biotin is obtained the need forchemical resolution is obviated. However, in instances where the racemicproduct is prepared the d-biotin is obtained by conventional resolutionprocedures.

SUMMARY OF THE INVENTION

This invention is directed to a process for synthesizing d-biotin, whichhas the structural formula: ##STR1## from cysteine, a compound of theformula: ##STR2##

DETAILED DESCRIPTION OF THE INVENTION

The term "alkyl" as used herein, denotes straight or branched chainhydrocarbon groups of 1 to 20 carbon atoms which are saturated or whichinclude one or more double and/or triple carbon to carbon bonds, such asmethyl, ethyl, allyl, propargyl, hexenyl and decyl. The term"cycloaliphatic" denotes monocyclic groups of 3 to 7 carbon atoms andpolycyclic groups of 5 to 17 carbon atoms, which are saturated or whichcontain double and/or triple carbon to carbon bonds, such as menthyl,bornyl and cholesteryl.

As further used throughout this applicatiion, the term "lower alkyl"denotes straight chain and branched chain saturated aliphatic groupshaving from 1 to 8 carbon atoms, such as methyl, ethyl, propyl,isopropyl, butyl, isobutyl and the like. As also used herein, the term"aryl" signifies mononuclear aromatic groups, such as phenyl, which canbe unsubstituted or substituted in one or more positions with a loweralkylenedioxy, a halogen, a nitro, a lower alkyl or a lower alkoxysubstituent and polynuclear aryl groups of 10 to 17 carbon atoms, suchas naphthyl, anthryl, phenanthryl and azulyl, which can be substitutedwith one or more of the aforementioned groups. The preferred aryl groupsare the substituted and unsubstituted mononuclear aryl groups,particularly phenyl. As further used herein, the term "aryl lower alkyl"comprehends groups wherein aryl and lower alkyl are as defined above,particularly benzyl. As still further herein, the term "lower alkoxy"comprehends alkoxy groups having from 1 to 7 carbon atoms such asmethoxy, ethoxy and the like. Also herein, the term "halogen" or "halo", unless otherwise stated, comprehends fluorine, chlorine, bromine andiodine. Further herein, the term "lower alkylenedioxy" comprehends loweralkylenedioxy groups having 1 to 4 carbon atoms, such as methylenedioxyand ethylenedioxy. The term "alkali" or "alkaline earth metals" denotessodium, potassium or lithium and calcium, barium or magnesium,respectively. The term "lower alkanols" refers to alkanols having alkylgroups (as defined above) of from 1-8 carbon atoms. The term "loweralkanoic" acid refers to monocarboxylic acids having from 1-8 carbonatoms. The term "lower alkyne" denotes a triply bonded alkyl groupcontaining 1-8 carbon atoms.

As still further used throughout this application, in the pictorialrepresentations of the compounds of this application, a thickenedtapered line ( ) indicates a substituent which is in the β-orientation(above the plane of the molecule), a dotted line ( - - - ) indicates asubstituent which is in the α-orientation (below the plane of themolecule) and a wavy line ( ) indicates a substituent which is in eitherthe α- or β-orientation.

In accordance, with the instant invention, d-biotin is prepared fromcysteine in conformity with the following scheme: ##STR3## wherein R ishydrogen or lower alkyl, R₁ is methyl or --CH₂ OR₄ where R₄ is loweralkyl or benzyl, R₂ is lower alkyl, R₃ is lower alkyl or substituted andunsubstituted aryl and X is halogen. Although the above reaction schemeis rather specific, the novel process is in no way to be construed aslimiting thereto.

Cysteine is converted to a sulfide of formula II in the above scheme bytreatment of the former with an alkyne having at least six carbon atoms.1-Hexyne is particularly preferred.

The conversion of cysteine to the sulfide of formula II is accomplishedby treating the compound of formula I with a lower alkyne, preferably1-hexyne, in an inert solvent in the presence of a free radicalinitiator. The reaction is carried out at atmospheric pressure and at atemperature sufficient to cause the formation of free radicals,generally from about 50° C. to about 100° C., preferably 60°-75° C.Typical solvents that may be employed are dioxane, tetrahydrofuran(THF), dimethylformamide (DMF), tetramethylurea, hexamethylphosphoricacid triamide (HMPA). Typical free radical initiators that may beemployed are azobisisobutyronitrile (AIBN), peroxides such as di-t-butylperoxide, benzoyl peroxide, cumyl hydroperoxide and the like.

The sulfide of formula II is then converted to the urethane of formulaIII in the above scheme by treatment of compound II with an aryl or alower alkyl haloformate such as methyl chloroformate, ethyl, isopropyl,phenyl or benzyl chloroformates, methyl chloroformate is particularlypreferred. This conversion takes place in an inert solvent underconditions of atmospheric pressure and a temperature varying from 0° C.to about 40° C., preferably at about room temperature. The inertsolvents that may be employed are those mentioned hereinabove.Tetrahydrofuran is particularly preferred. The conversion is generallycarried out under basic conditions. Typical bases that may be employedare alkali metal hydroxides, carbonates and bicarbonates. Sodiumcarbonate and potassium bicarbonate are particularly preferred. Organicamine bases such as lower alkyl amines, i.e., triethylamine,heterocyclic amines, such as pyridine, s-collidine and the like may alsobe used.

The compound of formula III is reduced to an aldehyde of formula IV. Thereduction is conducted in the presence of an inert solvent employingreducing agents that will selectively reduce the ester group to itscorresponding aldehyde. Particularly preferred reducing agents aredialkylaluminum hydrides, particularly diisobutylaluminum hydride(DiBAL) and Li(-3-t-butoxy)AlH₄. The reduction is carried out atatmospheric pressure and at temperatures varying from -65° C. to -85°C., preferably -70° C. to -80° C. The inert solvents that may beemployed are hexane, heptane, octane, toluene and the like.

The aldehyde of formula IV is then transformed to the isoxazolidines offormula V by treatment of the aldehyde of formula IV with either a loweralkyl or substituted and unsubstituted arylalkyl hydroxylamine. Althoughany substituted arylalkylhydroxylamine may be employed,benzylhydroxylamine is particularly preferred. The conversion of thealdehyde to the isoxazolidines of formula V proceeds by a 1,3-dipolaraddition which results in the formation of a 5,5-bicyclic ring system.This conversion affords predominately intermediates having the propersteric configuration which, upon further conversion(s), as detailedbelow, will result in all cis d-biotin. The transformation of compoundIV to compound V results in four isomers (Va to Vd). The ratio ofisomers Va+Vb to Vc+Vd is 62:38. This is a particularly attractivefeature of this synthesis because isomers Va and Vb possess the desiredall cis thiophane configuration for ultimate obtention of thebiologically active biotin. The conversion of the aldehyde to theisoxazolidines takes place in an inert solvent at atmospheric pressureand the reflux temperatures of the solvent. Typical solvents that may beemployed are benzene, toluene, xylene, heptane, hexane and the like.

The isoxazolidines of formula Va and Vb are then converted to thetetrahydrothiophenes of formula II by treating said isoxazolidines witheither DiBAL or Zn/lower alkanoic acid to effect the ring opening. Theconversion, when using Zn/lower alkanoic acid, takes place atatmospheric pressure and at temperatures ranging from 70° C.-100° C.,preferably 75° C.-80° C., using the excess lower alkanoic acid from theZn/lower alkanoic acid catalyst system or a mixture of lower alkanoicacid and water. The preferred lower alkanoic acid is acetic acid. WhenDiBAL is used to effect the conversion, atmospheric pressure andtemperatures of about -65° C. to about -85° C., preferably -75° C., areemployed.

The tetrahydrothiophenes of formula VI are then cyclized to theimidazolones of formula VII. The cyclization is conducted in thepresence of an alkali or alkaline earth metal hydroxide at atmosphericpressure and the reflux temperature of the solvent. The preferred baseis barium hydroxide, usually used as the monohydrate. The cyclizationmay be carried out in an inert solvent such as dioxane, tetrahydrofuranor mixtures of either of said ethers with water and the like.

The imidazolones of formula VII are then dehydrated to the imidazolonesof formula VIII. The dehydration is conducted in an inert solvent suchas benzene, toluene, hexane, heptane, xylene and the like at atmosphericpressure and at temperatures that may be determined by those skilled inthe art. Typically employed as dehydration agents are p-toluene sulfonicacid, sulfuric acid, P₂ O₅, SOCl₂, H₃ PO₄, activated alumina.Particularly preferred is p-toluenesulfonic acid at the refluxtemperature of the solvent.

The imidazolone of formula VIII is then reduced to an imidazolone offormula IX. The reduction of the compound of formula VIII to formula IXis accomplished using Raney nickel, Raney cobalt, supported palladium orplatinum--with the support preferably being carbon. This reduction iscarried out in a lower alkanol, preferably methanol under hydrogenpressure varying from about 100 psig to about 500 psig preferably 200psig and at room temperature.

The imidazolone of formula IX is then treated with Na/NH₃, or boilingHBr to form the imidazolone of formula X. The conversion of compound IXto compound X is carried out at atmospheric pressure and at atemperature varying from -50° C. to about -90° C., preferably -70° C.The conversion is generally carried out in an inert solvent such asdioxane, THF, and the like.

Compound X may be obtained directly from compound VIII by treating thelatter compound with either Raney nickel or palladium on carbon. Thedirect transformation of compound VIII to compound X may be accomplishedunder similar conditions employed for the transformation of compoundVIII to compound IX.

The conversion of compound X to biotin may be effected in one of twoways depending on the nature of the substituent R. When R is methylcompound X is converted to biotin by microbiological oxidationtechniques. The preferred microbiological oxidation is that disclosed inOgino et al., U.S. Pat. No. 3,859,167, the disclosure of which isincorporated herein by reference. In the Ogino et al. procedure,compound X where R is methyl is converted to biotin by treatment withthe organism

Corynebacterium Primorioxydans

When R is --CH₂ OR, with R₁ being as previously defined, compound X isconverted to biotin by converting the ether to an alcohol byconventional procedures for removing the ether protecting groups. Thealcohol that is then formed is converted to the corresponding aldehydeby treatment of said alcohol with Cr₂ O₃ /pyridine followed by oxidationto the corresponding lower alkanoic acid with Ag₂ O.

The preparation of biotin from cysteine as described hereinbeforerepresents an improvement over the biotin synthesis from cysteinedisclosed in Confalone et al., U.S. Pat. No. 3,957,794. The instantprocedure is shorter, has significantly higher step yields through theentire procedure than does the aforementioned Canfalone process.

The following non-limiting examples are illustrative of the instantinvention. All temperatures are in degrees Centigrade.

EXAMPLE 1

A mixture of 12.80 g (68.93 mmol) of DL-cysteine ethyl esterhydrochloride, 25.60 g (311.62 mmol) of 1-hexyne, and 50 mg of2,2'-azobis-(2-methylpropionitrile) in 250 ml of absolute dioxane wasstirred at 60°-65°. under inert gas atmosphere for 20 minutes. Aftercooling, most of the solvent was evaporated in vacuo. The residue wastreated with 150 ml of 1 N sodium carbonate solution and extracted threetimes with ethyl acetate. The organic phases were combined, washed with3×50 ml of saturated brine, dried over anhydrous sodium sulfate andevaporated in vacuo to give 15.90 g (99%) of crude (ethyl2-aminopropanoate-3-yl) (1-hexenyl) sulfide as a thick pale yellow oilwhich can be used without further purification in the next step. NMRspectroscopical studies showed that the product is approximately a 1:1mixture of geometrical isomers.

EXAMPLE 2

To a solution of 15.90 g (68.72 mmol) of (ethyl 2-aminopropanoate-3-yl)(1-hexenyl) sulfide obtained from Example 1 dissolved in 100 ml oftetrahydrofuran, 200 ml of a 2 N potassium bicarbonate solution and 200ml of a 2 N sodium carbonate solution was added. The mixture was cooledat 0° C. and 19.50 g (206.34 mmol) of methyl chloroformate was addeddropwise under stirring over the period of 30 minutes. After addition,the reaction mixture was allowed to come to room temperature and furtherstirred for 2 hours. It was then extracted three times with ethylacetate and the combined organic phases were washed three times withsaturated brine, dried over anhydrous sodium sulfate and evaporated invacuo to give 17.80 g (89.5%) of crude (ethyl2-methoxycarbonylaminopropanoate-3-yl)(1-hexenyl)sulfide. This waspurified on a 385 g. silica column, using ethyl acetate/hexane aseluent, to give 10.40 g (52.3%) of pure product.

EXAMPLE 3

To a solution of 4.06 g (14.02 mmol) of the (ethyl2-methoxycarbonylaminopropanoate-3-yl)(1-hexenyl)sulfide obtained fromExample 2 dissolved in 60 ml of absolute toluene cooled at -70° to -78°C., 20.6 ml. (30.0 mmol) of a solution of diisobutylaluminum hydride intoluene (containing 1.5 mmol/ml) precooled at -70° to -78° C. was addeddropwise under inert gas atmosphere and over a 30 minute period. At theend of the addition, the reaction mixture was further stirred at -70° to-78° C. for 30 minutes. After this time, 50 ml of a saturated ammoniumchloride solution was slowly added dropwise to the reaction mixturewhich was then allowed to come to room temperature and then extractedthree times with ethyl acetate. The combined organic phases were washedthree times with saturated brine, dried over anhydrous sodium sulfate,filtered through "celite" and evaporated in vacuo. The residue wasdissolved in 50 ml of dichloromethane, filtered through "celite" andevaporated in vacuo to give 3.33 g (97%) of crude(2-methoxycarbonylaminopropanol-3-yl)(1-hexenyl) sulfide which can beused as such in the next step.

EXAMPLE 4

A solution of 3.34 g (13.61 mmol) of(2-methoxycarbonylaminopropanol-3-yl)(1-hexenyl)sulfide obtained fromExample 3 and 1.68 g (13.64 mmol) of benzylhydroxylamine in 70 ml ofabsolute benzene was refluxed in a Dean Stark moisture receiverapparatus. The solvent was then evaporated in vacuo and the mixture ofisomeric isoxazolidines obtained was first purified on a 100 g silicacolumn using a mixture of hexane and ethyl acetate (1:1) as eluent togive 3.56 g (74.6%) of a mixture of Va, Vb, Vc, Vd. The components ofthe mixture were then separated by high pressure liquid chromatographyusing a Waters Associates chromatograph Model 202 and an 8'×3/8" PORASISA^(R) column, eluted with a mixture of hexane and ethyl acetate (5:1) togive the following isomers:

(a) 0.869 g of pure[3R,6S,3S,6R-(3α,3aβ,6β,6aβ)]-3-butyl-3a,5-6,6a-tetrahydro-1-(phenylmethyl)-6-[(methoxycarbonyl)amino]-1H,3H-thieno[3,2-c]isoxazole(Va). Crystallization from hexane affordedwhite crystals: m.p. 106°-107° C.

Anal. Calcd for C₁₈ H₂₆ N₂ O₃ S: C, 61.69; H, 7.48; N, 7.99. Found: C,61.88; H, 7.51; N, 7.99,

(b) 1.202 g of pure[3S,6S,3R,6R-(3β,3aβ,6β,6aβ)]-3-butyl-3a,5,6,6a-tetrahydro-1-(phenylmethyl)-6-[(methoxycarbonyl)amino]-1H,3H-thieno[3,2-c]isoxazole(Vb).Recrystallized from hexane, gave white crystals; m.p. 106°-107° C.

Anal calcd for C₁₈ H₂₆ N₂ O₃ S: C, 61.69; H, 7.48; N, 7.99. Found: C,61.90; H, 7.70; N, 7.69,

(c) 0.419 g of pure[(3S,6S,3R,6R-(3β,3aα,6β6aα)]-3-butyl-3a,5,6,6a-tetrahydro-1-(phenylmethyl)-6-[(methoxycarbonyl)amino]-1H,3H-thieno[3,2-c]isoxazole(Vd).Crystallized from hexane, gave white crystals: m.p. 67°-68° C.

Anal calcd for C₁₈ H₂₆ N₂ O₃ S: C, 61.99; H, 7.48; N, 7.99. Found: C,61.70; H, 7.53; N, 7.94, and

(d) 0.805 g of pure[3R,6S,3S,6R-(3α,3aα,6β,6aα)]-3-butyl-3a,5,6,6a-tetrahydro-1-(phenylmethyl)-6-[(methoxycarbonyl)amino]-1H,3H-thieno[3,2-c]isoxazole(Vc).Crystallized from hexane, gave white crystals: m.p. 107°-107.5°.

Anal. Calcd for C₁₈ H₂₆ N₂ O₃ S: C, 61.69; H, 7.48; N, 7.99. Found: C,61.76; H, 7.63; N, 7.69.

EXAMPLE 5

A suspension of 0.576 g (1.64 mmol) of the isoxazole (a) of Example 4,1.5 g of zinc dust in 20 ml of 50% acetic acid was stirred at 75°-80°0C. for 20 hours. The reaction mixture was then filtered and the solventevaporated in vacuo. The residue was treated with 50 ml of a 2 N sodiumcarbonate solution which was then extracted three times with ethylacetate. The combined organic phases were washed three times withsaturated brine, dried over anhydrous sodium sulfate, filtered, andevaporated to dryness to give 0.566 g (98% yield) of crude[2R-(2R*),3R,4S,2S-(2S*),3S,4R]-α-butyltetrahydro-4-[(methoxycarbonyl)amino]-3-[(phenylmethyl)amino]-2-thiophenemethanol.Crystallization from ether afforded 0.508 g (89% yield) of pure product,m.p. 88°-89° C.

Anal. Calcd for C₁₈ H₂₈ N₂ O₃ S: C, 61.33; H, 8.01; N, 7.95.

Found: C, 61.41; H, 8.21; N, 7.61.

EXAMPLE 6

A suspension of 0.905 g (2.58 mmol) of the product (b) of Example 4, 2.0g of zinc dust in 40 ml of 50% acetic acid was stirred at 75°-80° C. for20 hours. The reaction mixture was then filtered and the solventevaporated in vacuo. The residue was treated with 50 ml of a 2 N sodiumcarbonate solution which was then extracted three times with ethylacetate. The combined organic phases were washed three times withsaturated brine, dried over anhydrous sodium sulfate, filtered, andevaporated to dryness to give 0.902 g (99% yield) of crude[2R-(2S*),3R,4S,2S-(2R*)3S,4R]-α-butyltetrahydro-4-[(methoxycarbonyl)amino]-3-[(phenylmethyl)amino]-2-thiophenemethanol.Crystallization from ether gave 0.849 g (93% yield) of pure product,m.p. 121°-122° C.

Anal. Calcd. for C₁₈ H₂₈ N₂ O₃ S: C, 61.33; H, 8.01; N, 7.95. Found: C,61.42; H, 8.14; N, 7.82.

EXAMPLE 7

A mixture of 0.820 g (2.32 mmol) of the product of Example 5, 2.0 g ofbarium hydroxide monohydrate, 30 ml of water, and 20 ml of dioxane wasrefluxed for 2 hours. After cooling, the reaction mixture was saturatedwith sodium chloride and extracted four times with ethyl acetate. Thecombined organic phases were washed three times with saturated brine,dried over anhydrous sodium sulfate, and evaporated in vacuo to give0.650 g (87%) of crude [4R,4S-(3aβ,4β(R*), (S*),6aβ)]-3a,4,6,6a-tetrahydro-4-(1-hydroxypentyl)-3-(phenylmethyl)-1H-thieno[3,4-d]imidazol-2(3H)-one.Crystallization from ether-methylene chloride gave 0.569 g (66%) of pureproduct, m.p. 174°-175° C.

Anal. Calcd for C₁₇ H₂₄ N₂ O₂ S: C, 63.72; H, 7.55; N, 8.74. Found: C,63.88; H, 7.73; N, 8.86.

EXAMPLE 8

A mixture of 0.888 g (2.52 mmol) of the product of Example 6, 1.5 g ofbarium hydroxide monohydrate, 30 ml of water, and 25 ml of dioxane wasrefluxed for 11/2 hours. After cooling, the reaction mixture wasacidified with 2 N hydrochloric acid and extracted three times withethyl acetate. The combined organic phases were washed three times withsaturated brine, dried over anhydrous sodium sulfate, and evaporated invacuo and crystallized from ether-methylene chloride to give 0.741 g(92%) of pure[4R,4S-(3aβ,4β(S*),(R*),6aβ)]-3a,3,6,6a-tetrahydro-4-(1-hydroxypentyl)-3-(phenylmethyl)-1H-thieno[3,4-ol]imidazole-2(3H)-one,m.p. 190°-191° C.

Anal. Calcd for C₁₇ H₂₄ N₂ O₂ S: C, 63.72; H, 7.55; N, 8.74. Found: C,63.55; H, 7.60; N, 8.81.

EXAMPLE 9

A solution of 0.400 g (1.25 mmol) of the product Example 7 0.356 mg(1.87 mmol) of p-toluenesulfonic acid in 40 ml of absolute toluene wasrefluxed for 9 hours. After cooling, the reaction mixture was dilutedwith 100 ml of ethyl acetate washed with three times each 2 N sodiumcarbonate solution and saturated brine, dried with anhydrous sodiumsulfate, filtered, and evaporated in vacuo to give 0.395 g of crude[4R,4S-(3aβ,4β,6aβ)]-3a,4,6,6a-tetrahydro-3-(phenylmethyl)-4-(1-pentyl)-1H-thieno[3,4-d]imidazol-2(3H)-one.Two crystallizations from ether afforded 0.149 g (40%) of pure product,m.p. 92°-93° C. The mother liquors still contain large amounts ofproduct together with the corresponding cis isomer, which can be used assuch in the next step.

Anal. Calcd for C₁₇ H₂₂ N₂ OS: C, 67.51; H, 7.33; N, 9.26. Found: C,67.45; H, 7.12; N, 9.09.

EXAMPLE 10

A solution of 0.727 g (2.27 mmol) of the product of Example 8, 0.615 g(3.23 mmol) of p-toluenesulfonic acid in 60 ml absolute toluene wasrefluxed for nine hours. After cooling the reaction mixture was dilutedwith 100 ml. of ethyl acetate, washed three times each with a 2 N sodiumcarbonate solution and saturated brine, dried with anhydrous sodiumsulfate, filtered, and evaporated in vacuo to give 0.678 g of crudeproduct. This was crystallized twice from ether to give 0.391 g (57%yield) of pure product. The mother liquor still contains large amountsof product together with its corresponding cis isomer which can be usedas such in the next step.

EXAMPLE 11

A suspension of 0.235 g (0.78 mmol) of the product of Examples 9 and 10,150 mg. of 10% palladium-on-charcoal in 50 ml of methanol washydrogenated at room temperature and under 200 lbs. pressure for 20hours. The reaction mixture was then filtered and evaporated in vacuo togive 0.227 g of crude[4R,4S-(3aβ,4β,6aβ)]-3a,4,6,6a-tetrahydro-3-(phenylmethyl)-4-pentyl-1H-thieno3,4-d imidazol-2(3H)-one. Crystallization from ether-methylene chloridegave 0.195 g (82%) of white crystals, m.p. 129°-131° C.

Anal. Calcd for C₁₇ H₂₄ N₂ OS: C, 67.07; H, 7.94; N, 9.20. Found: C,66.76; H, 7.88; N, 9.21.

EXAMPLE 12

To a solution of 0.100 g (0.328 mmol) of the product of Example 11, 10ml of absolute tetrahydrofuran and 20 ml of liquid ammonia (distilledfrom sodium) kept at -70° C., small pieces of sodium were continuouslyadded during 1 hour, so that the blue color of the solution persists.After this time, a few crystals of ammonium chloride were added untilthe blue color disappears. Then again, small pieces of sodium wereadded, until the blue color of the solution persists for three hours.After that, a few crystals of ammonium chloride were added and thereaction mixture allowed to come to room temperature and the ammonia toevaporate. The residue was treated with 50 ml of saturated ammoniumchloride solution and extracted three times with ethyl acetate. Thecombined organic phases were washed three times with brine, dried overanhydrous sodium sulfate, filtered, and evaporated in vacuo to give0.070 g of crude[4R,4S-(3aβ,4β,6aβ)]-3a,4,6,6a-tetrahydro-4-pentyl-1H-thieno[3,4-d]imidazol-2(3H)-one. Crystallization from methylene chloride gave0.057 g (81%) of white crystals, m.p. 144°-145° C.

Anal. Calcd for C₁₀ H₁₈ N₂ OS: C, 56.04; H, 8.46; N, 13.07. Found: C,55.96; H, 8.33; N, 12.63.

We claim:
 1. A compound of the formula: ##STR4## the enantiomers andracemates thereof, wherein R₁ is methyl or --CH₂ OR₄, where R₄ is loweralkyl or benzyl; R₂ is lower alkyl and R₃ is phenyl, naphthyl, benzyl;said phenyl or naphthyl each are unsubstituted or substituted with ahalogen, lower alkylenedioxy having 2 to 5 carbon atoms, lower alkyl orlower alkoxy, with the lower alkyl and lower alkoxy moieties each having1 to 7 carbon atoms.
 2. The compound of claim 1 wherein R₁ and R₂ aremethyl and R₃ is phenyl.
 3. A compound of the formula: ##STR5## theenantiomers and racemates thereof, wherein R₁ is methyl or --CH₂ OR₄,where R₄ is lower alkyl or benzyl; R₂ is lower alkyl and R₃ is phenyl,naphthyl, benzyl; said phenyl or naphthyl each are unsubstituted orsubstituted with a halogen, lower alkylenedioxy having 2 to 5 carbonatoms, lower alkyl or lower alkoxy, with the lower alkyl and loweralkoxy moieties each having 1 to 7 carbon atoms.
 4. The compound ofclaim 3 wherein R₁ and R₂ are methyl and R₃ is phenyl.